Multiprocessor Qbus PDP-11

Alan Frisbie Flash688 at
Fri Aug 20 14:41:09 CDT 2021

Charles Dickman <chd at> wrote:

 > There are indications in the KDJ11-B processor spec on bitsavers that
 > the M8190 could be used in a multiprocessor configuration. For
 > example, bit 10 of the Maintenance Register (17 777 750) is labeled
 > "Multiprocessor Slave" and indicates that the bus arbitrator is
 > disabled. There is also section 6.6, "Cache Multi-Processor Hooks",
 > that describes cache features that allow multiprocessor operation.
 >Would it be as simple as connecting to 11/83 qbus together? And adding
 > the proper software.
 > Anybody ever heard of such a thing?

Such a system was put together and tested at DEC with the RSX group
(who did the PDP-11/74 multiprocessor work).  I'm told that while it
worked, it wasn't terrible successful, and the project was abandoned.

I was given a gift of one of the CPU modules that was used in the test
and I might still have it around here.  I can't recall for certain,
but I think the module required some ECOs to make it work in a
multi-processor configuration.

The person to ask about this, Brian McCarthy, is unfortunately no
longer with us.  :-(

Alan Frisbie

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